1. Field of the Invention
The present invention relates to a method for forming a capacitor of a semiconductor device, and more particularly to a method for forming a capacitor of a semiconductor device capable of improving the film quality of a dielectric film.
2. Description of the Prior Art
As the design rule of memory semiconductor devices becomes smaller, the height of the capacitor (i.e., the electrode height) is continuously increased and the thickness of the dielectric film is reduced to obtain desired charging capacity. This is because the charging capacity is proportional to the area of the electrodes and the dielectric constant of the dielectric film and is inversely proportional to the thickness of the dielectric film corresponding to the gap between the electrodes. Since increase in the electrode height is limited, particularly, recent researches to secure sufficient charging capacity are directly to reducing the thickness of the dielectric film and developing new dielectric film.
In addition, researches to secure sufficient charging capacity are directed not only to the development of a dielectric film itself, but also to using metal as the electrode material, instead of polysilicon. When Ta205 film is used as the dielectric material, for example, decrease in thickness of the dielectric film made of Ta205 results in increase of leak current if the electrode material is polysilicon. However, if the electrode is metal, both charging capacity and leak current characteristics can be secured by reducing the effective oxide film thickness (Tox), even when the thickness of the dielectric film made of Ta205 decreases.
In order to secure sufficient charging capacity to meet the trend of high integration of memory semiconductor devices, therefore, it is inevitable to use a metal electrode. A conventional method for forming an Metal/lnsulator/Metal (MIM) capacitor will now be described with reference to FIGS. 1A to 1C, which are sectional views thereof.
Referring to FIG. 1A, an etching stop nitride film 4 is formed on a semiconductor substrate 1 having an interlayer insulation film 2 and a storage node contact 3 formed in the interlayer insulation film 2. A spacer (not shown) made of nitride material is formed on the lateral surface of the storage node contact 3. A cap oxide film 5 is formed on the etching stop nitride film 4. A photoresist pattern 6 is formed on the cap oxide film 5 to define a region in which a storage electrode is to be formed.
Referring to FIG. 1B, the photoresist pattern is used as an etching mask to etch the cap oxide film 5 and the etching stop nitride film 4 to form a hole exposing the storage node contact 3. The photoresist pattern is removed and a metal silicide film, e.g., a titanium silicide film 7 is formed on the surface of the exposed storage node contact 3 in a conventional process.
Referring to FIG. 1C, a metal storage electrode 8 made of, e.g., titanium nitride, is formed on the hole surface including the titanium silicide film 7. A dielectric film 9 and a metal plate electrode 10 are successively formed on the front surface of the substrate including the metal storage electrode 8 to complete the formation of an MIM capacitor 12.
As for the dielectric film of the MIM capacitor 12, a single film made of HfO2 or Al2O3 having large dielectric constant or a lamination film made of both is generally used.
Although the charging capacity (Cs) and leak current characteristics required in devices of 100-80 nm grade may be satisfied to some degree by using a material having large dielectric constant as the dielectric film and forming a capacitor in MIM structure, it is difficult to satisfy both charging capacity and leak current characteristics as desired, if the design rule of semiconductor devices further decreases in the future, with a material having large dielectric constant as mentioned above. This means that film quality of the dielectric film must be additionally improved.